The invention relates to a power generation system with a relay arrangement for disconnecting the system from a three-phase grid. The invention also relates to an inverter for providing power to a three-phase grid, and a corresponding relay arrangement.
Power generation systems are used to provide electrical power to a grid. Their importance is increasing as natural resources to run large power plants are limited and becoming more expensive. One example of such a system is an inverter, which may be used to convert a direct current (DC) into an alternating current (AC), and typically includes a semiconductor bridge circuit that functions as a DC-AC converter.
The direct current may come from any DC source such as a battery, for example. The DC source may be a photovoltaic generator that is used to feed energy into a grid.
Photovoltaic inverters intended for installation on relatively small surfaces should be as compact, easy to handle, and as lightweight as possible to minimize the need for tools during installation. Such inverters should have weight and dimensions that allow one to two people to transport and install them largely unaided.
The necessary electronic components, semiconductors, filter chokes, capacitors, and similar elements are contained within the housing. An increase in the permissible output power of the device may result in an increase in the dimensions of the individual components. Therefore, a device or its housing must be as tightly equipped as possible if it is to be compact.
To receive approval for grid parallel feeding, the applicable standards and regulations (e.g. DIN V VDE V 0126-1-1) require that power generation systems are to be connected to the grid via an automatic switching circuit. The main purpose of this device is to prevent unintentional feeding into a sub-grid or stand-alone grid, often referred to as anti-islanding, and hence serves a protective function.
To eliminate the need for an additional housing or additional installation aids, the switching circuit may be integrated into the existing inverter housing. However, this increases the size of the housing.
The aforementioned standard also requires that this switching circuit is able to interrupt the feed in process for each active conductor via two serially connected and independently activated switches. The disconnection is to be established in such a way as to ensure the safety function, even in the event of a single error.
A common practice for meeting this requirement is to use a single-pole relay with sufficient switching capacity for medium power ranges up to 10 kW or higher. This relay usually includes an independent controller and corresponding monitoring device.
Three-pole relays or contactors are only available for higher power ranges and require significantly more installation space than printed circuit board (PCB) relays. Furthermore, their assembly is labor-intensive, error-prone, and unsuitable for large-batch production. A standards-compliant solution would therefore require the use of six single-pole relays, which is not only costly but also takes up installation space.
According to an aspect of the invention, a power generation system for feeding electrical power from a generation unit into a three-phase grid via three AC terminals is provided. The system includes a relay arrangement for disconnecting the inverter from the grid. The relay arrangement includes at least three relays, each of which is equipped with a control coil and two switching contacts operated by the control coil. Each AC terminal of the system is connectable to the grid via a first and a second switching contact, each of which is assigned to a different one of the relays.
The system may include an inverter, such as a photovoltaic inverter, in particular a transformerless photovoltaic inverter. The relay arrangement may be integrated into the system's housing, and may be arranged on a circuit board of the system, thus leading to a compact system design.
In a further aspect of the invention, an inverter for converting a DC power into an AC power provided to a three-phase grid via three AC terminals is provided. The inverter includes a relay arrangement for disconnecting the inverter from the grid. The relay arrangement includes at least three relays, each of which includes a control coil and two switching contacts operated by the corresponding control coil. Each AC terminal is connectable to the grid via a first and a second switching contact, each of which is assigned to a different one of the relays.
In yet a further aspect, a relay arrangement for disconnecting an inverter from a three-phase grid with three active conductors is provided. The relay arrangement includes at least three relays, each of which includes a control coil and two switching contacts operated by the corresponding control coil. Each switching contact is connected to another switching contact that is assigned to a different one of the relays.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
The drawings below provide a more detailed description of the invention, and are intended to illustrate specific embodiments. They are not intended to limit the scope of the invention.